The use of coiled tubing (CT) technology in oil and gas drilling and servicing has become more and more common in the last few years. In CT technology, a continuous pipe wound on a spool is straightened and pushed down a well using a CT injector. CT technology can be used for both drilling and servicing.
The advantages offered by the use of CT technology, including economy of time and cost are well-known. As compared with jointed-pipe technology wherein typically 30–45 foot straight sections of pipe are connected one section at a time while drilling the well bore, CT technology allows the continuous advancement of piping while drilling the well significantly reducing the frequency with which such drilling must be suspended to allow additional sections of pipe to be connected. This results in less downtime, and as a result, an efficiency of both cost and time.
However, the adoption of CT technology in drilling has been less widespread than originally anticipated as a result of certain problems inherent in using CT in a drilling application. For example, because CT tends to be less robust than jointed-pipe for surface-level drilling, it is often necessary to drill a pilot hole using jointed-pipe, cement casing into the pilot hole, and then switch over to CT drilling. Additionally, when difficult formations such as boulders or gravel are encountered down-hole, it may be necessary to switch from CT drilling to jointed-pipe drilling until the formation is overcome, and then switch back to CT drilling to continue drilling the well. Similarly, when it is necessary to perform drill stem testing to assess conditions downhole, it may again be necessary to switch from CT drilling to jointed-pipe drilling and then back again. Finally, a switch back to jointed-pipe operations may be necessary to run casing into the drilled well. These types of situations require the drilling manager to switch back and forth between CT drilling rigs and jointed-pipe drilling rigs, a process which results in significant down-time as one rig is moved out of the way, and another rig put in place.
Another disadvantage of CT drilling is the time-consuming process of assembling a BHA (bottom-hole-assembly—the components at the end of the CT for drilling, testing, etc.), and connecting the BHA to the end of the CT. Presently, this step is performed manually through the use of rotary tables and make/breaks. Not only does this process result in costly down-time, but it can also present safety hazards to the workers as they are required to manipulate heavy components manually.